Rigid body simulation requires mass input every time
Rigid body always need mass to work properly.

You can`t apply forces to 0 mass rigid body.

Rigid-body dynamics studies the movement of systems of interconnected bodies under the action of external forces. The assumption that the bodies are rigid, which means that they do not deform under the action of applied forces, simplifies the analysis by reducing the parameters that describe the configuration of the system to the translation and rotation of reference frames attached to each body.

Wikipedia

EDIT

Try if this Works